Glycogen synthase kinase 3 (GSK3) is a serine/threonine protein kinase composed of two isoforms (α and β), which are encoded by distinct genes but are highly homologous within the catalytic domain. GSK3 is highly expressed in the central and peripheral nervous system. GSK3 phosphorylates several substrates including tau, β-catenin, glycogen synthase, pyruvate dehydrogenase and elongation initiation factor 2b (eIF2b). Insulin and growth factors activate protein kinase B, which phosphorylates GSK3 on serine 9 residue and inactivates it (Kannoji et al, Expert Opin. Ther. Targets 2008, 12, 1443-1455).
Alzheimer's Disease (AD) Dementias, and Taupathies.
AD is characterized by cognitive decline, cholinergic dysfunction and neuronal death, neurofibrillary tangles and senile plaques consisting of amyloid-β deposits. The sequence of these events in AD is unclear, but is believed to be related. Glycogen synthase kinase 3β (GSK3β), or Tau phosphorylating kinase, selectively phosphorylates the microtubule associated protein Tau in neurons at sites that are hyperphosphorylated in AD brains. Hyperphosphorylated tau has lower affinity for microtubules and accumulates as paired helical filaments, which are the main components that constitute neurofibrillary tangles and neuropil threads in AD brains. This results in depolymerization of microtubules, which leads to dying of axons and neuritic dystrophy. (Hooper et al., J. Neurochem. 2008, 104(6), 1433-1439). Neurofibrillary tangles are consistently found in diseases such as AD, amyotrophic lateral sclerosis, parkinsonism-dementia of Guam, corticobasal degeneration, dementia pugilistica and head trauma, Down's syndrome, postencephalatic parkinsonism, progressive supranuclear palsy, Niemann-Pick's Disease and Pick's Disease. Addition of amyloid-β to primary hippocampal cultures results in hyperphosphorylation of tau and a paired helical filaments-like state via induction of GSK3β activity, followed by disruption of axonal transport and neuronal death (Imahori and Uchida, J. Biochem. 1997, 121, 179-188), while GSK3α has been postulated to regulate the production of amyloid-β itself (Phiel et al. Nature, 2003, 423, 435-439). GSK3β preferentially labels neurofibrillary tangles and has been shown to be active in pre-tangle neurons in AD brains. GSK3 protein levels are also increased by 50% in brain tissue from AD patients. Furthermore, GSK3β phosphorylates pyruvate dehydrogenase, a key enzyme in the glycolytic pathway and prevents the conversion of pyruvate to acetyl-Co-A (Hoshi et al., PNAS 1996, 93: 2719-2723). Acetyl-Co-A is critical for the synthesis of acetylcholine, a neurotransmitter with cognitive functions. Accumulation of amyloid-β is an early event in AD. GSK transgenic mice show increased levels of amyloid-β in brain. Also, PDAPP(APPV717F) transgenic mice fed with lithium show decreased amyloid-β levels in hippocampus and decreased amyloid plaque area (Su et al., Biochemistry 2004, 43, 6899-6908). Likewise, GSK3β inhibition has been shown to decrease amyloid deposition and plaque-associated astrocytic proliferation, lower tau phosphorylation, protect against neuronal cell death, and prevent memory deficincies in a double APPsw-tauvlw mouse model (Serenó et al, Neurobiology of Disease, 2009, 35, 359-367). Furthermore, GSK3 has been implicated in synaptic plasticity and memory function (Peineau et al., Neuron 2007, 53, 703-717; Kimura et al., PloS ONE 2008, 3, e3540), known to be impaired in AD patients.
In summary, GSK3 inhibition may have beneficial effects in progression as well as the cognitive deficits associated with Alzheimer's disease and other above-referred to diseases.
Acute Neurodegenerative Diseases
Growth factor mediated activation of the PI3K/Akt pathway has been shown to play a key role in neuronal survival. The activation of this pathway results in GSK3β inhibition. GSK3β activity is increased in cellular and animal models of neurodegeneration such as cerebral ischemia or after growth factor deprivation (Bhat et al., PNAS 2000, 97, 11074-11079). Several compounds with known GSK3β inhibitory effect has been shown to reduce infarct volume in ischemic stroke model rats. A recent publication (Koh et al, BBRC 2008, 371, 894-899) demonstrated that GSK-3 inhibition decreased the total infarction volume and improved neurobehavioral functions by reducing ischemic cell death, inflammation, brain edema, and glucose levels, in a focal cerebral ischemia model. Thus GSK3β inhibitors could be useful in attenuating the course of acute neurodegenerative diseases.
Bipolar Disorders (BD)
Bipolar Disorders are characterized by manic episodes and depressive episodes. Lithium has been used to treat BD based on its mood stabilizing effects. The disadvantage of lithium is the narrow therapeutic window and the danger of overdosing that can lead to lithium intoxication. The discovery that lithium inhibits GSK3 at therapeutic concentrations has raised the possibility that this enzyme represents a key target of lithium's action in the brain (Stambolic et al., Curr. Biol. 1996, 68, 1664-1668; Klein and Melton; PNAS 1996, 93, 8455-8459; Gould et al., Neuropsychopharmacology, 2005, 30, 1223-1237). GSK3 inhibitor has been shown to reduce immobilization time in forced swim test, a model to assess on depressive behavior (O'Brien et al., J Neurosci 2004, 24, 6791-6798). GSK3 has been associated with a polymorphism found in bipolar II disorder (Szczepankiewicz et al., Neuropsychobiology. 2006, 53, 51-56) Inhibition of GSK3β may therefore be of therapeutic relevance in the treatment of BD as well as in AD patients that have affective disorders.
Schizophrenia
Accumulating evidence implicates abnormal activity of GSK3 in mood disorders and schizophrenia. GSK3 is involved in signal transduction cascades of multiple cellular processes, particularly during neural development. (Kozlovsky et al., Am. J. Psychiatry, 2000, 157, 831-833) found that GSK3β levels were 41% lower in the schizophrenic patients than in comparison subjects. This study indicates that schizophrenia involves neurodevelopmental pathology and that abnormal GSK3 regulation could play a role in schizophrenia. Furthermore, reduced β-catenin levels have been reported in patients exhibiting schizophrenia (Cotter et al., Neuroreport 1998, 9, 1379-1383). Atypical antipsychotic such as olanzapine, clozapine, quetiapine and ziprasidone, inhibits GSK3 by increasing ser9 phosphorylation suggesting that antipsychotics may exert their beneficial effects via GSK3 inhibition (Li X. et al., Int. J. of Neuropsychopharmacol, 2007, 10, 7-19).
Diabetes
Type 2 diabetes mellitus is characterized by insulin resistance and β-cell failure. Insulin stimulates glycogen synthesis in skeletal muscles via dephosphorylation and thus activation of glycogen synthase and therefore increased glucose disposal. Under resting conditions, GSK3 phosphorylates and inactivates glycogen synthase via dephosphorylation. GSK3 is also over-expressed in muscles from Type II diabetic patients (Nikoulina et al., Diabetes 2000 February; 49(2), 263-71) Inhibition of GSK3 increases the activity of glycogen synthase thereby decreasing glucose levels by its conversion to glycogen. In animal models of diabetes, GSK3 inhibitors lowered plasma glucose levels up to 50% (Cline et al., Diabetes, 2002, 51: 2903-2910; Ring et al., Diabetes 2003, 52, 588-595). Moreover, results obtained by using haploinsufficient GSK3β mice on a diabetic background indicated that reduced GSK3β activity also protects from β-cell failure (Tanabe et al., PloS Biology, 2008, 6(2), 307-318 GSK3 inhibition may therefore be of therapeutic relevance in the treatment of Type I and Type II diabetes to enhance insulin sensitivity and reduce β-cell failure and therefore also relevant therapy to reduce diabetic complications like diabetic neuropathy.
Alopecia
GSK3 phosphorylates and degrades β-catenin. β-Catenin is an effector of the pathway for keratonin synthesis. β-Catenin stabilization may be lead to increase hair development. Mice expressing a stabilized β-catenin by mutation of sites phosphorylated by GSK3 undergo a process resembling de novo hair morphogenesis (Gat et al., Cell, 1998, 95, 605-14)). The new follicles formed sebaceous glands and dermal papilla, normally established only in embryogenesis. Thus, GSK3 inhibition may offer treatment for a variety of indications that lead to alopecia.
Inflammatory Disease
The discovery that GSK3 inhibitors provide anti-inflammatory effects has raised the possibility of using GSK3 inhibitors for therapeutic intervention in inflammatory diseases. (Martin et al., Nat. Immunol. 2005, 6, 777-784; Jope et al., Neurochem. Res. 2007, 32, 577-595). Inflammation is a common feature of a broad range of conditions including Alzheimer's Disease and mood disorders. A recent publication (Kitazawa et al, Ann. Neurol. 2008, 64, 15-24) indicates that GSK3β may play a role in inclusion body myositis (IBM).
Cancer
GSK3 is over expressed in ovarian, breast and prostate cancer cells and recent data suggests that GSK3β may have a role in contributing to cell proliferation and survival pathways in several solid tumor types. GSK3 plays an important role in several signal transduction systems which influence cell proliferation and survival such as WNT, PI3 Kinase and NFkB. GSK3β deficient MEFs indicate a crucial role in cell survival mediated NFkB pathway (Ougolkov A V and Billadeau D D., Future Oncol. 2006 February, 2(1), 91-100). Thus, GSK3 inhibitors may inhibit growth and survival of solid tumors, including pancreatic, colon and prostate cancer. Growth control of multiple myeloma cells has been demonstrated through inhibition of GSK3 (Zhou et al 2008 Leuk. Lymphoma, 48, 1946-1953). A recent publication (Wang et al, Nature 2008, 455, 1205-1209) demonstrated that GSK3 inhibition was efficacious in a murine model of MLL leukemia. Thus, GSK3 inhibitors may also inhibit growth and survival of hematological tumors, including multiple myeloma.
Glaucoma
There is a possibility of using GSK3 inhibitors for therapeutic treatment of glaucoma. Elevated intraocular pressure (IOP) is the most significant risk factor for the development of glaucoma, and current glaucoma therapy focuses on reducing IOP, either by reducing aqueous humor production or by facilitating aqueous humor outflow. Recently published expression profiling experiments (Wang et al., J. Clin. Invest. 2008, 118, 1056-1064) have revealed that the soluble WNT antagonist sFRP-1 is over expressed in ocular cells from glaucoma patients relative to control subjects. A functional link between WNT signaling pathways and glaucoma was provided through experiments in which addition of recombinant sFRP-1 to ex vivo-cultured human eye anterior segments resulted in a decrease in aqueous humor outflow; in addition, in vivo experiments in mice demonstrated that over expression of sFRP-1 in ocular tissues resulted in increases in intraocular pressure, an effect that was antagonized by a small-molecule GSK3 inhibitor. Taken together, the results reported by Wang et al. (2008) suggest that activation of WNT signaling via inhibition of GSK3 may represent a novel therapeutic approach for lowering intraocular pressure in glaucoma.
Pain
A recent publication (WO2008/057933) indicates that GSK3beta inhibitors may play a role in the treatment of pain, particularly neuropathic pain, by modulation of glycogenolysis or is glycolysis pathways.
Bone-Related Disorders and Conditions
Genetic studies have established a link between bone mass in humans and Wnt signaling (Gong et al., Am. J. Hum. Genet. 1996, 59, 146-51, Little et al., N. Engl. J. Med., 2002, 347, 943-4). Genetic and pharmacological manipulations of Wnt signaling in mice have since then confirmed the central role of this pathway in regulating bone formation. Of the pathways activated by Wnts, it is signaling through the canonical (i.e., Wnt/β-catenin) pathway that increases bone mass through a number of mechanisms including renewal of stem cells, stimulation of pre-osteoblast replication, induction of osteoblastogenesis, and inhibition of osteoblast and osteocyte apoptosis. Therefore, enhancing Wnt pathway signaling with GSK3 inhibitors alone or in combination with a suitable device could be used for the treatment of bone-related disorders, or other conditions which involve a need for new and increased bone formation for example osteoporosis (genetic, iatrogenic or generated through aging/hormone imbalance), fracture repair as a result of injury or surgery, chronic-inflammatory diseases that result in bone loss such as for example rheumatoid arthritis, cancers that lead to bone lesions, such as for example cancers of the breast, prostate and lung, multiple myeloma, osteosarcoma, Ewing's sarcoma, chondrosarcoma, chordoma, malignant fibrous histiocytoma of the bone, fibrosarcoma of the bone, cancer induced bone disease, iatrogenic bone disease, benign bone disease and Paget's disease.
Regenerative Medicine
Stem-cell expansion and differentiation are required for self-renewal and maintenance of tissue homeostasis and repair. The β-catenin-mediated canonical Wnt signaling pathway has been shown to be involved in controlling stem differentiation (Pinto et al., Exp. Cell Res., 2005, 306, 357-63). A physiological Wnt response may be essential for the regeneration of damaged tissues. GSK3 inhibitors by enhancing Wnt signaling may be useful to modulate stem cell function to enhance tissue generation ex vivo or in vivo in diseases associated with tissue damage or reduced tissue repair.
WO2007/040440, published Dec. 4, 2007, relates to imidazole and phenyl substituted pyrimidine compounds that are stated to have a selective inhibiting effect at GSK3 as well as a good bioavailability.